The gathering house price gloom and the weakness of sterling have shackled young foreign professionals plotting to escape the new tax on non-doms.

The £30,000 annual charge on non-doms, which came into effect last month, may be a trifle for the super-wealthy but it weighs heavily on the thousands of middle-ranking workers earning up to £300,000 who live and work in Britain but who declare that their true home is elsewhere.

Those who wish to take their leave of London are discovering that the values of their swish £1 million to £2 million properties in the best postcodes have slumped, as the housing market nationwide goes into decline.

Halifax reported yesterday that prices fell by 1.3 per cent in April, the fourth consecutive decrease. The drop in the value of the pound against the euro – 20 per cent since September – will reduce further the amount of capital that the departing non-dom takes home if he or she is returning to Paris, Berlin, Milan or Madrid.

Ed Mead, of the Chelsea office of Douglas & Gordon, the estate agent, already sees signs that some non-doms are being thwarted in their attempt to seek their fortunes elsewhere. He said: “These guys are finding out that they will not get the big money for their flats in Kensington and Chelsea that they were hoping for. They’re facing a double whammy. If they can get a buyer, the price may be 10 to 15 per cent less. Then they take another hit on the sterling-euro exchange rate.”

London properties are under pressure both from the effects of the credit crunch and also from fears of more City job losses. The prices of apartments in the smartest streets of Chelsea have been creeping down since the beginning of the year, with the typical non-dom twentysomething bachelor pad slipping from £1.3 million to £1.1 million.

Yolande Barnes, residential research director of Savills, the estate agent, forecast that the £1-£2 million section of the market could decline by as much 15 per cent this year if the credit crunch continues to make mortgages scarce. Ms Barnes believes that the whole market could drop by up to 25 per cent if the credit crunch carries on until the end of 2009.

Hometrack, Nationwide and Halifax all recorded price falls and fewer transactions; the average house price is £189,027. This is £10,573 lower than at the market’s peak in August 2007.

However, Martin Ellis, Halifax’s chief economist, also emphasises that prices trebled in the ten years to August 2007. Halifax figures were published as the lender continued to restrict the supply of affordable finance, the principal cause of the market’s malaise. The bank announced it will bar all new customers from taking out its standard variable rate (SVR) deal from today, blocking off a lifeline to those who are struggling to remortgage.

SVR loans are traditionally the most expensive type of mortgage deal for homeowners. However, as fixed and tracker rates have risen, SVRs – which do not involve expensive arrangement fees – have begun to look cheaper, becoming more popular with cash-strapped borrowers.

Halifax’s SVR went down from 7.25 per cent to 7 per cent last month, when the Bank of England base rate dropped to 5 per cent. Brokers said that the move was a way for Halifax to shield itself from further cuts in the base rate.

Aaron Strutt, of Chase De Vere Mortgage Management, the broker, said: “Unlike fixed rates, lenders are expected to decrease their SVRs in line with the base rate. Halifax clearly does not want a lot of borrowers on a rate that could keep going down and carries no fees for applying or exiting the deal, as this will lose them money.”

A spokeswoman for Halifax said: “We are now seeing a very significant increase in the number of new customers opting to take an SVR mortgage with us”. But she added that there were “administrative costs involved in setting up a mortgage and then seeing the customer depart soon afterwards”.